In fluorescence-based imaging, a fluorescing material present in a field of view of an imaging device is excited with light of one wavelength and emits light of a different wavelength. This may provide a useful mechanism for highlighting portions of the field of view that are of particular interest to the observer. For example, in the case of fluorescence image-guided surgery, a fluorescent dye, such as indocyanine green (ICG) may be introduced to portions of a patient's anatomy to highlight those portions of the patient's anatomy. When ICG is excited with near-infrared light (approximately 750-800 nm), it fluoresces with a slightly higher wavelength (around 845 nm). By introducing ICG into selected portions of the patient's anatomy, the surgeon or other medical personnel, with the aid of a suitable viewer or camera, may receive visual cues and/or highlights that help them identify and/or avoid the selected anatomy. For example, ICG or other dyes may be used to highlight sentinel lymph nodes, areas of relative perfusion, tumor margins, and/or the like. Other useful fluorescent dyes suitable for highlighting patient anatomy include methylene blue, fluorescein, and IRDye® from LI-COR, Inc. of Lincoln, Nebr. In some cases, the fluorescence may be in the visible band, and may not require an extra viewer or camera. While fluorescence-based imaging is being used, it is also common to use visible-light to generally illuminate other regions of the patient's anatomy about the region of interest or fluorescence so that the surgeon and/or other medical personnel may see and visualize other anatomical structures.
Unfortunately, fluorescence-based imaging is susceptible to many of the same problems as other imaging applications. Many portions of a patient's anatomy are highly reflective of light due to, for example, the presence of moisture on the surface of anatomical structures, such as tissue and/or organ structures. Because of this high reflectance, the visual light being used to generally illuminate the patient's anatomy may generate one or more areas of high specular reflection. These areas of high specular reflection may create bright spots in the images of the patient's anatomy and/or saturate the sensors used to detect the images. As a result, the areas of high specular reflection may be mistaken for fluorescing areas and/or mask or obscure the areas of fluorescence, thus limiting the usefulness of the fluorescence in detecting the selected anatomy.
Accordingly, it is desirable to provide improved methods and systems for detecting, reducing, and/or compensating for areas of high specular reflection so that a more useful fluorescence image may be obtained.